Dr. Ron Milo and research students Niv Antonovsky and Lior Zelcbuch of the Plant Sciences Department turned their sights on astaxanthin because the algae that produce it are hard to cultivate, and they require special conditions to make the metabolite. For Milo and his group, this was a side project. They are working with the bacterium E. coli to see if they can coax it to absorb carbon dioxide from the atmosphere, as plants do. The scientists use E. coli – the workhorse of the genetic engineering field – because its genome is well known and easy to manipulate. Convincing the bacteria to produce astaxanthin would be a sort of test case for some cutting-edge methods of genetic engineering the scientists are using in experiments.

 

In other words, a good deal of fine-tuning is needed. To achieve the best levels of efficiency, the researchers applied genetic engineering techniques to a number of genes at once in the E. coli. From this they obtained thousands of different strains, from which they could select those with the desired properties. To adjust the output of the steps in the metabolic pathway they used a sort of “volume control button” on each gene. This is a segment at the beginning of the gene that gives instructions to the ribosome – the cellular factory that translates the genetic information to proteins. Small changes in the sequences of these segments can lead to significant differences in the intensity of gene expression.

 

To begin with, the research team generated random mutations in the “volume control buttons” of the genes involved in astaxanthin production and then inserted these genes into E. coli. The bacteria in their lab dishes began to produce engineered enzymes, and these, in turn, produced the different intermediate metabolites on the astaxanthin metabolic pathway.

 

How did the team identify the strains that produced astaxanthin the most efficiently? Here nature came to the scientists’ aid: Astaxanthin is pink, and thus the bacterial colonies that were the loveliest pink color were those that had the most finely tuned metabolic pathways for its production. The most promising strains then underwent biochemical analysis to quantify astaxanthin levels. The best of these was found to yield over five times as much astaxanthin as other research groups around the world had managed to produce through metabolic engineering in bacteria. These results recently appeared in Nucleic Acids Research.

Milo and his group believe that this method could be used, in the future, in metabolic engineering to improve efficiency in the production of bioactive substances and drugs.
 

Dr. Ron Milo's research is supported by the Mary and Tom Beck-Canadian Center for Alternative Energy Research; the Lerner Family Plant Science Research Endowment Fund; the European Research Council; the Leona M. and Harry B. Helmsley Charitable Trust; Dana and Yossie Hollander, Israel; the Jacob and Charlotte Lehrman Foundation; the Larson Charitable Foundation; the Wolfson Family Charitable Trust; Charles Rothschild, Brazil; Selmo Nissenbaum, Brazil; the Anthony Stalbow Charitable Trust; and the estate of David Arthur Barton.  Dr. Milo is the incumbent of the Anna and Maurice Boukstein Career Development Chair in Perpetuity.

 

We all know how hard it is to shift an economy from stagnation to growth, but in nature, a transition of this kind occurs on a routine basis – whenever plant seeds shift from a dormant state to that of germination.

 

This transition calls for sudden, far-ranging changes in all the plant’s systems: The plant’s entire genome undergoes reprogramming that affects the expression of genes and the manufacture of proteins. Hundreds of proteins – those that help the seed develop and block premature germination – stop being produced, whereas the production of hundreds of other proteins – those needed for germination – is set in motion.

“The germination revolution” plays a crucial role both in nature and in agriculture because it has an enormous impact on the harvest. Generally, the greater the proportion of germinating seeds and the faster their germination, the bigger the harvest. In fact, farmers use various methods to stimulate germination artificially – for example, by soaking dry seeds for a short while in a germination-promoting solution. Understanding germination on the molecular and metabolic levels is, therefore, vitally important: It can lead to sophisticated ways of improving the rate and speed of germination, thereby increasing crop harvest. Moreover, it can help control the precise timing: When the seeds germinate too early, while still attached to the parent plant and before they reach the soil, they are unlikely to develop into new plants.
 

 

Prof. Gad Galili of the Weizmann Institute’s Plant Sciences Department has conducted pioneering studies on the “germination revolution.” He has recently discovered that a molecular process called selective autophagy, which is central to the plant’s life, also takes part in controlling the germination.

In general, autophagy, which means “self-eating,” involves the dismantling of proteins, and it occurs in numerous organisms; originally discovered in yeast, it exists also in animals, including human beings. Autophagy has been the subject of extensive studies – among other reasons because in humans, defects in selective autophagy are implicated in Alzheimer’s, Parkinson’s and other common diseases. In the plant world, the main function of autophagy is to save the plant in times of trouble. Since plants, unlike animals, cannot run away from danger, their survival depends on flexible mechanisms that help them cope with mortal threats by other means. Large-scale autophagy, for instance, can prevent plant death when nutrients are in short supply.

Lately, however, it has become clear that selective autophagy, in which individual proteins or other cellular components are dismantled without connection to distress or danger, takes place in plants at certain times, including the preparation for germination. Galili has discovered about ten genes that might be involved in selective autophagy in plants. In studies published this year in The Plant Cell and other journals, he has focused on two of these genes, ATI1 and ATI2, which are unique to plants – that is, they do not exist in animals.
 

 

 

 

In experiments with the model plant Arabidopsis, Galili and his team have shown that enhancing the expression of ATI1 stimulates germination. When this gene’s activity increased, so did the proportion of germinating seeds; moreover, these seeds germinated faster. The scientists hypothesize that ATI1 and ATI2 promote germination by dismantling proteins that block this process. When the scientists blocked the activity of the two genes, ATI1 and ATI2, germination was reduced. In addition to clarifying the roles of these genes, the scientists also obtained further details about their functioning – for example, where exactly in the plant cell their activity takes place. Prof. Galili’s team included postdoctoral fellow Dr. Arik Honig and graduate student Tamar Avin-Wittenberg.

The study of selective autophagy in plants is still in its infancy, but unraveling it in greater detail should enable plant researchers to improve plant growth and crop yields by enhancing seed germination on demand.

 

Prof. Gad Galili’s research is supported by the Lerner Family Plant Science Research Endowment Fund; and the Adelis Foundation. Prof. Galili is the incumbent of the Bronfman Professorial Chair of Plant Science.
 

 

 

Improve speed on the Piccadilly Line, create delays on the track to Hyde Park Corner, route more trains through Kings Cross. These are not suggestions for baffling passengers of the London Underground. Rather, it’s a metaphor describing how plant scientists may one day breed new varieties: To enhance the breeding process, they may consult plant metabolism models that resemble the familiar map of the London Tube.
 

 

Creating such metabolic models, which simulate the network of biochemical reactions in the plant, is extremely challenging because plant metabolism involves thousands of enzymes and is extremely complex. A new plant metabolic model, the most complete to date, has recently been created by a team headed by scientists from the Weizmann Institute, the Technion – Israel Institute of Technology and Tel Aviv University. This computerized model, described in the Proceedings of the National Academy of Sciences, USA, focuses on Arabidopsis, a plant in the mustard family that is commonly used in research. The network of this plant’s metabolic reactions is so wide and branched that it indeed evokes the layout of an extensive underground system, in which the lines represent the pathways of metabolic reactions, the trains symbolize individual enzymes and the ends of the lines – the reactions’ end products.